Bent bamboo · kit design log
One socket, four angles, and rods that push back.
A printed PLA joint system for quarter inch bamboo: 6.35 mm rods, sold everywhere as 610 mm sticks. Every socket is the same socket, so any joint mates with any joint, and the whole system is designed around bending the rod rather than keeping it straight. This page is the design log, not a shop.
Design only, as of 2026-08-02. Nothing has been printed, no fit coupon has run on these parts, and nothing has been assembled.
The bore constants carry over from this project's earlier printed bamboo work, the stave shelf gauge and the stand. Every fit is machine and depth conditional, so on these sockets they are guesses with good ancestry until a coupon prints. The ledger below keeps that line visible.
One socket, everywhere
The LEGO trick was never the brick, it is the stud: one interface repeated without exception, so every part is compatible with every part by construction. Here the interface is a socket, 12 mm deep, in two fits. Snug is a 7.05 bore, the middle hole of a three-bore gauge printed in July and picked by hand on a real 6.35 rod. Slide is 7.65, sized from the same gauge work plus the room a hot round bore needs before a rod will move in it. Every socket on every part is one of those two.
Through every socket runs a 3 mm cross hole. It is a drill guide first: seat the rod, run a 3 mm bit through the hole and through the captive rod, then push a standard bamboo skewer through boss, rod and boss. The skewer is a shear pin: the rod cannot pull out or spin, no glue anywhere, and the pin is the same material as the frame. The workflow this enables is the point: friction fit while you experiment, take it apart freely, then pin only the joints you decide to keep. A structure graduates one skewer at a time and stays disassemblable by pulling pins. Bent rods are why it is not optional: a bowed rod pushes outward against its sockets forever, and the pin guarantees that push can never walk the rod out.
Angles are quantized to 45, 60, 90 and 120 degrees. Four angles cover square frames, triangulated frames and hex layouts, and quantization is the compatibility: any part meets any part at an angle both already agree on. The one exception is the 15 degree end joint, and the next section is why it exists.
socket · bore 7.05 snug or 7.65 slide, 12 mm deep, both carried constants
pin · 3 mm cross hole through every socket, a bamboo skewer is the pin
angles · 45 / 60 / 90 / 120, plus the 15 degree arc absorber
The bend is the point
Straight-stick construction sets exist everywhere. This one assumes the rod arrives bent. The limit is known from the stave shelf's geometry work: a 6.35 rod snaps below roughly a 318 mm bend radius, a figure computed from literature bamboo properties, not yet measured on these sticks. The kit's standard arcs stay at radius 1000 and up, at least three times outside the snap radius, so a rod on a kit arc is loafing.
A bowed rod does not meet its socket square. On the reference arc, a 32 mm bow over a 521 mm chord for a radius of 1079, the rod arrives about 14 degrees off the socket axis. The 15 degree end joint exists for exactly that: it absorbs the arrival angle by design instead of asking a straight socket to take it as a side load.
The reward for tolerating all this is preload. A bowed rod pushes outward against its sockets for as long as it stays bowed, so a preloaded frame cannot rattle: the slop is spent permanently. That physics is worked through, on paper and in emitted geometry, in the stave shelf design. The built precedent this kit actually leans on is the ball lift, whose frame is quarter inch bamboo held by printed joints and standing. Bowed preload itself has not been assembled by anyone here yet, and the ledger says so.
Kit v1: ten parts, one interface
Every part below is the same socket repeated at quantized angles. No part has a special interface, which is the whole idea.
- inline sleeve · two sockets at 180. Extends a rod or splices a broken one.
- L90 · the square corner.
- T · a 90 degree branch off a running rod.
- X · a full cross, four ways in one plane.
- Y120 · three ways at 120, the hex corner.
- rosette hub · six sockets at 60 in one plane. The wheel centre.
- 3D node · sockets out of the plane, takes a flat frame into the third axis.
- saddle clamp · grips a bowed rod mid arc and adds a branch, no unthreading.
- 15 degree end joint · the arc absorber. A bowed rod lands in it square.
- foot cap · closes a rod end and gives it a floor to stand on.
What is carried in, and what is not proven
✓ Measured or built before
- The snug bore: 7.05 was picked by hand off a printed three-bore gauge on a real 6.35 rod, July 2026.
- Printed PLA joints holding a quarter inch bamboo frame: the ball lift is built and standing on them.
- The bend arithmetic: arc margins and the 14 degree arrival, measured from the stave shelf's emitted geometry. The 318 snap radius is computed from literature values, one grade weaker.
○ Not proven yet
- Nothing on this page has been printed. No joint, no coupon, no pin.
- Both bores at this 12 mm depth on this machine. Fits are machine and depth conditional, and the 7.65 slide has never itself been picked off a gauge.
- Bowed preload in a printed socket. The stave shelf that works it through is itself unprinted; the claim rests on arithmetic and straight-rod precedent.
- The saddle clamp's grip on a live arc, and a 3 mm skewer pin under load.
- The 15 degree end joint seating a real bowed rod: chord geometry so far, not an assembly.
Reproduce it
The kit is generated by a dependency-free Python script in the public crackle repository: one socket definition, every part derived from it. It emits binary STLs, and a separate gate re-measures watertightness and printability off the emitted mesh, because a generator's own summary is not evidence.
qa_stl.py · the gate: watertight, printable, bed fit. It fails loudly or it passes.